The surfaces of aqueous phases and films have unique kinetics and thermodynamics, distinct from the bulk. However, major surface analytical techniques are mostly vacuum-based and direct applications for volatile liquid studies are difficult. We developed a vacuum compatible microfluidic interface, System for Analysis at the Liquid Vacuum Interface (SALVI), to enable direct observation of liquid surfaces and liquid-solid interactions. The unique aspects of this R&D 100 award winner include the following: 1) the detection window is an aperture of 2-3 μm in diameter allowing direct imaging of the liquid surface, and 2) surface tension is used to hold the liquid within the aperture. SALVI is composed of a silicon nitride (SiN) membrane and polydimethylsiloxane (PDMS). Its applications in time-of-flight secondary ion mass spectrometry (ToF-SIMS) as an analytical tool were evaluated using a variety of aqueous solutions and complex liquid mixtures, some of which contain nanoparticles. Recently, we demonstrated <i>in situ</i> probing of the electrode-electrolyte solution interface (or solid-electrolyte interface, SEI) using a new electrochemical SALVI. It provides the first direct observation of the surface and diffused layer of SEI in a liquid with chemical speciation using ToF-SIMS. Moreover, SALVI was extended for biofilm growth and mammalian cell cultures and correlative imaging by more than one spectroscopy and microscopy technique. SALVI was also used to investigate solvent structure of switchable ionic liquids. Results from our latest development will be presented in addition to published ones, showcasing new directions and applications of multimodal imaging of environmental surfaces and interfaces and studying chemistry from the bottom up, all based on microfluidics.

In situ probing of environmental liquid surfaces and interfaces by time-of-flight secondary ion mass spectrometry

249th National Meeting (2015)

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